Traditionally, an LCD (Liquid Crystal Display) panel is illuminated by a backlight module for increasing the screen bright of the LCD panel to enhance the display quality.
FIG. 1 illustrates a driving architecture of a backlight module of a conventional LCD. As shown in FIG. 1, an inverter 101 is used to supply a potential to each lamp 111, 113, 115 and 117 of the backlight module 110 to switch on these lamps. The potential outputted from the inverter 101 is a sine wave wherein the voltage varies as a function of time, whereas the output frequency is constant. As such, the signal transmitted from the inverter 101 through the backlight module 110 to the LCD panel would result in the ripple noise where an interference noise would be periodically generated on the display image.
The cause of the ripple noise is briefly summarized herein. Generally, the voltage supplied to the backlight module 110 (such as lamps 111, 113, 115 and 117) is much greater than the voltage for driving each pixel of the LCD panel. Therefore, the voltage of each pixel of the LCD panel is interfered by the voltage supplied from the inverter 101 to the backlight module 110. In this case, the potential of each pixel corresponding to the respective lamps 111, 113, 115 and 117 of the backlight module 110 would exhibit a potential distribution having a sine waveform along the longitudinal direction, thereby generating dark band(s) on the display image. As shown in FIG. 2A, the dark bands 210 are appeared on the LCD panel 200.
Generally, the potential difference between the adjacent dark bands 210 is quite small, and therefore, the dark bands 210 instantaneously appeared on the image are not readily perceived by the user with naked eyes. Yet, according to the display principle of the LCD panel 200, a timing controller (not shown in figure) is used for sequentially providing potential to each pixel of the LCD panel 200, from top to bottom.
As described hereinabove, the potential supplied from the inverter 101 to the backlight module 110 would propagate as a sine wave. As such, if the image illustrated in FIG. 2A is the image displayed by the LCD panel 200 at the 1st second, then, at the 2nd second, since the supplied potential capable of affecting the potential of each pixel of the LCD panel 210 would propagate downward, the image displayed by the LCD panel 200 would be the one illustrated in FIG. 2B, wherein the dark band 211 is located under the dark band 210 shown in FIG. 2A. As discussed hereinabove, the dark band 210 (or 211) shown on the momentary image would not be perceived by a user with naked eyes. Yet, when the images are displayed continuously, the dark band appeared to be moving downward, for example, the position of the dark band shifts from the dark band 210 to the dark band 211 shown in FIG. 2C, thereby resulting in the ripple noise that could be perceived by a user with naked eyes. As such, the image quality of the LCD would be deteriorated.
Therefore, a driving architecture of the backlight module of the LCD is disclosed in U.S. Pat. No. 6,417,833, entitled “Liquid Crystal Display Apparatus and Method for Lighting Backlight thereof”. FIG. 3 is a schematic diagram illustrating such driving architecture. The first inverter 103 outputs potential driving voltage to the lamp 1111 and the lamp 1113, and the second inverter 105 outputs potential driving voltage to the lamp 1115 and the lamp 1117. In the instant example, the potentials outputted from the first inverter 103 and the second inverter 105 have a phase difference of 180 degrees; that is, a positive-potential high voltage is applied to the lamp 1111 and 1113, whereas a negative-potential high voltage is applied to the lamp 1115 and 1117. As such, the dark bands generated by the lamp 1113 and 1115 are offset by the compensation provided by the 180-degree phase difference. However, the instant architecture is not able to effectively reduce the dark bands generated between the lamps 1111 and 1113 and between the lamps 1115 and 1117. Moreover, during the startup of the lamps, the high voltage difference between the positive and negative potentials simultaneously generated by two adjacent lamps may cause the problem of flashover.
An improvement to the driving architecture illustrated in FIG. 3 is disclosed in Taiwan Patent No. I240599, entitled “Lamp Module and Backlight Module”, wherein an alternative arrangement is provided to reduce the chances where the positive and negative potentials are neighboring, thereby reducing the probability of the flashover. However, although the driving architecture disclosed in this patent can reduce the chance of the flashover, a dark band would still be generated when the potentials of two adjacent lamps have the same phases. In other words, if the voltages received by the adjacent lamps have the same phases, a dark band would be generated.
In view of the foregoing, the prior art fails to effectively reduce the ripple noise of a display image of the LCD panel caused by the driving inverter of the backlight module.
Accordingly, there exists a need in the art for a method for reducing the ripple noise of the display image of an LCD panel caused by the interference of the potential outputted from the driving inverter of the backlight module. Also, the method is capable of improving the display quality of the LCD without substantially altering the driving architecture of the LCD.